Blast gas heating



Nov. 9, 1965 s. VAJDA ETAL BLAST GAS HEATING 2 Sheets-Sheet 1 Filed Sept. 21, 1961 INVENTORS Stephen Vajda By William H. Ceckler their ATTORNEY Nov. 9, 1965 s. VAJDA ETAL 3,216,709'

BLAST GAS HEATING Filed Sept. 21, 1961 2 Sheets-Sheet 2 INVENTORS Stephen Va j do BY WILLIAM H. Ceckler their ATTORNEY- United States Patent 3,216,709 BLAST GAS HEATING Stephen Vajda, OHara Township, and William H. Ceclrler, Osborne, Pa, assignors to Jones & Laughlin Steel Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 21, 1961, Ser. No. 139,743 2 Claims. (Cl. 26319) This invention relates to the heating of blast gas. It is particularly concerned with apparatus for heating to high temperatures blast gas for iron blast furnaces and the like.

Blast furnaces for the smelting of iron are blown with air which has been previously heated to temperatures of 1000 degrees to 1500 degrees F. The air is conventionally heated in regenerative stoves. These stoves burn blast furnace gas with air under pressure, the products of combustionbeing passed through a checker work of refractory brick to heat that checker work. After a stove has been heated up in this fashion, the heating gas is cut off and cold blast is passed through the hot stove, absorbing heat from the checkers. Each blast furnace is normally provided with three or four stoves which alternatively receive and give off heat.

A conventional blast furnace stove is a cylindrical structure 100 feet or more in height and to 28 feet in diameter. Its interior is divided by a vertical partition into a relatively small empty columnar combustion chamber of to about 55 square feet cross section, depending on the stove diameter, and a relatively larger checker chamber, which chambers communicate wtih each other at their upper ends. At the bottom of the combustion chamber a gas burner is movably positioned in the stove wall. A stack or flue is connected into the checker chamber near its bottom. A blast inlet is also provided at the bottom of the checker chamber and a blast outlet at the bottom of the combustion chamber. When the stove is being heated, the blast inlet and outlet are closed. When the stove is on blast the flue is closed oif, the burner is pulled out of the combustion chamber and the opening therefor is closed by a gate.

Conventional burners for blast furnace stoves introduce the blast furnace gas and air for combustion as streams co-axial with the burner axis. There is no signaficant mixing of gas and air in the burner. The gas, at a pressure of 6 to 12 inches of water, mixes in the combustion chamber with air at the same pressure. The gas and air mixture burns with a long flame which extends well upward toward the top of that chamber. It has been found by experience that the heat input to the stove is limited by the cross-sectional area of the combustion chamber. Prior to our invention to be described, stoves were designed to burn 300 to 400 cubic feet per minute of blast furnace gas per square foot of combustion chamber cross-sectional area, although occasional stoves were capable of burning up to 600 cubic feet of gas per minute per square foot. When attempts were made to increase the gas input beyond that figure, the combustion was found to become pulsating, and the pulsations, if allowed to continue, built up in amplitude until they shook the stove, damaging its brick work, or blew out the flame. Unburned gas and air, if not shut olf, soon filled the stove with an explosive mixture. Reference to a possible cause of those pulsations is made hereinafter; the phenomenon, whatever its cause, is familiar to all blast furnace operators.

It has been observed that high blast temperatures increase the iron output of blast furnaces and also reduce their coke rate. It is possible to obtain a higher average 3,216,709 Patented Nov. 9, 1965 ice blast temperature from conventional stoves by reducing the time during which a stove is on blast, but unless the heating time for the stove can be decreased correspondingly, an additional stove is required. Some attempts have been made to obtain higher blast temperature by increasing the amount of checker work in a stove, and with improved blast furnace gas cleaning apparatus it is possible to reduce the size of the checker openings so as to increase the volume of the checkers holding heat. However, any reduction in the area through which the hot gases pass increases the back pressure against which the burners must operate. Prior to our invention the only feasible way to obtain higher temperatures appeared to be to construct larger stoves. Stoves, however, are so expensive as to be difficult to justify economically. Furthermore, many existing blast furnace installations do not have the extra room required for larger stoves.

It is an object of our invention, therefore, to provide blast gas heating apparatus of conventional size which is capable of heating blast to substantially higher temperatures than heretofore. It is another object to provide blast gas heating apparatus of conventional size capable of burn-ing blast furnace gas at much higher rates than has heretofore been possible. It is still another object to provide blast gas heating apparatus having the advantages above mentioned which can be incorporated into existing blast furnace stoves. Yet another object is to provide a means for the pulsation-free burning of gas in a columnar combustion chamber. Other objects of our invention will appear in the course of the description thereof which follows.

We have found that the rate of combustion of gas in a stove can be greatly increased by pre-mixing the gas and air and burning it turbulently in the stove combustion chamber. We have also found that the desired turbulence can be economically maintained by modifying the stove structure in a manner which will appear.

Our invention will be readily understood by reference to the attached figures which illustrate an embodiment thereof presently preferred by us.

FIGURE 1 is an elevation partly in section of a portion of the combustion chamber of a stove of our invention.

FIGURE 2 is a horizontal cross-section of the apparatus of FIGURE 1 on the plane IIII.

FIGURE 3 is another elevation of the apparatus of FIGURE 1.

FIGURE 4 is an elevation in section of a stove of our invention.

The stove 1 has a curved outer Wall 2. Inside the stove a curved vertical partition 3 divides the stove into a combustion chamber 4 and a checker chamber 5. Near the bottom of outer wall 2 of combustion chamber 4 is fitted a gas burner 6 so that the discharge end of the burner opens into combustion chamber 4. Above burner 6 is positioned a second burner 7. Burners 6 and 7 are preferably of the same type, to be described.

Burner 6 comprises a cylindrical housing 8 having a closed outer end 9. The housing is provided with a refractory lining 10. Through end 9 on the axis of housing 3 projects a conduit 11 through which air is introduced into the burner. Through the wall of housing 8 near its closed end 9 opens a conduit 12 through which blast furnace gas is introduced into the burner. The outer end of conduit 11 is connected to air supply line 15 through valve 14. The outer end of conduit 12 is connected to gas supply line 17 through valve 16.

Burner 6 is provided with an internal refractory sleeve 13 forming a passageway of small diameter than housing 8 which extends through the combustion chamber wall 2 and which stops short of end 9 a distance about equal to the diameter of gas conduit 12. Air conduit 11, which is of substantially smaller diameter than the passageway through sleeve 13, projects into the burner 6 through end 9 and terminates at about the inner end of sleeve 13. The annular chamber so formed adjacent end 9 is of greater diameter than the passageway through sleeve 13, but of shorter length. It provides a space within which the gas from conduit 12 swirls more or less spirally and converges therefrom through the restricted opening between conduit 11 and sleeve 13 toward the air stream moving through sleeve 13. The swirling gas stream mixes with the air stream within the passageway through sleeve 13.

Burner 7 is of the same type as burner 6 and therefore requires no further description. Both burners are connected to the same air supply line 15 and gas supply line 17. The two burners are positioned vertically one above the other as is shown in FIGURE 3 and each burner is positioned at an angle to wall 2 so that the flame from the burner is projected transversely of combustion chamber 4 and approximately tangent to partition wall 3, as is shown in FIGURE 2,

Stove 1 is covered with a domed top 13. The open space 19 under top 18 communicates with combustion chamber 4 and checker chamber 5, and provides a passageway therebetween for combustion gases and air. Checker chamber is filled with checkers 20 of re fractory material. At the bottom of checker chamber 5 a flue 21 provides for the withdrawal of gases from that chamber.

When a stove of our invention is to be heated, valves 14 and 16 are opened. Blast furnace gas is thereby admitted to burner 6 through conduit 12 and air for combustion is admitted through conduit 11. The streams of gas and air are admitted at substantially right angles to each other and mix within burner 6. The gas and air mixture from burner 6 burns at its discharge end in a turbulent fashion. The flame from burner 6 tends to whirl or rotate in a plane normal to its direction of travel and also to travel spirally up through the combustion chamber. The products of combustion from burner 6 impinge on the flame from burner 7, creating further turbulence therein. The result is that the combustion chamber 4 is filled with turbulent hot gases.

Burners Sand 7 are each constructed to burn gas at the rate of 20,000 cubic feet per minute. A burner of that size is about as large as can be physically installed in an average sized combustion chamber of about 35 square feet cross sectional area. Air and gas are supplied to the burners at pressures ranging from 1% pounds per' square inch to 2% pounds per square inch, or more (42 to 63 inches of water). The stove equipped with those burners thus burns gas at the rate of 40,000 cubic feet per minute, in a combustion chamber which by conventional standards is deemed adequate to burn gas at about 15,000 cubic feet per minute only. This increased heat input, which is obtained without pulsation, permits the stove to supply blast at a much higher temperature than before. One installation with which We are familiar comprises four stoves, each of which originally burned gas at about 15,000 cubic feet per minute. Those stoves provided blast at an average temperature of about 1150 degrees F. at a wind rate of 60,000 cubic feet per minute. One stove was modified in accordance with our invention as above described and the installation then supplied blast at an average temperature of 1600 degrees F. at the same wind rate.

Our invention may be embodied in a stove provided with three burners positioned one above the other as described, or even more, as conditions warrant.

It is our theory that the phenomenon of pulsation which. imposes a limit on the rate of firing of conventional stoves by conventional means is the result of reflected shock waves created by the burning of the gas and air in the combustion chamber. A simple compression wave in an unobstructed columnar combustion chamber travels along the length of the chamber. It is well known that in a straight pipe, either open or closed end, a wave initiated at one end will travel to the other end and will then be reflected back again. If the air or other gas in the pipe is continuously excited at a uniform rate and if the reflected waves are brought into phase with those being excited, the waves resulting are called standing waves because their regions of minimum and maximum amplitude are fixed. Because of their continuous reinforcement, standing waves can exert strong vibrational forces on the pipe walls. In the conventional firing of blast furnace stoves, the air and gas are introduced into the stove combustion chamber and there must mix before they will burn. No matter in what direction they may be introduced, they cannot mix until they have traveled some distance up the combustion chamber so that when they burn, the flame is propagated substantially axially of the combustion chamber. The combustion of the gas, therefore, produces simple compression waves which travel the length of the combustion chamber and are reflected in it just as in any other straight pipe. It would be expected therefore, that this combustion would result in mechanical vibration at a natural frequency of the combustion chamber.

The fundamental natural frequency of a straight openend pipe feet long is about 6 cycles per second. The frequencies of pulsation observed in conventional blast furnace stove operation are of that order of magnitude.

We find that by pre-mixing gas and air and introducing it transversely of the direct-ion of travel of simple compression waves in the combustion chamber, the flame, which begins to burn immediately adjacent the end of the burner, propagates transversely to that direction of travel. The compression waves which are generated are no longer simple compression waves travelling axially of the chamber but have very substantial components in other directions, which are reflected from the walls of the chamber. The resulting turbulence in the combustion chamber inhibits the formation of standing waves. This turbulence is increased by imparting a whirling movement to the flame and by causing the flame to travel spirally along the combustion chamber. Turbulence is also increased by burning the gas in two or more burners spaced from each other along the combustion chamber.

We claim:

1. In blast heating apparatus comprising a vertical elongated heat exchanging chamber filled with checker work of heat absorbing material and an unobstructed columnar combustion chamber having an outer wall, means for connecting the upper ends only of those chambers with each other, combustion gas supply means and combustion air supply means, the improvement comprising a plurality of gas burners set in the outer wall of the combustion chamber one above the other, at least one burner being a premixing burner of generally cylindrical form and having a chamber adjacent its closed end and a smaller diameter passage communicating therewith and opening into the columnar combustion chamber, an imperforate air inlet conduit of smaller diameter than the passage extending through the closed end of the burner into the chamber and terminating at about the junction of the chamber with the passage, and a gas inlet of smaller diameter than the passage opening radially into the wall of the chamber, the premixing burner being positioned to project a flame transversely of the combustion chamber.

2. Apparatus of claim 1 in which the combustion gas supply means for the premixing burner are adapted and adjusted to supply blast furnace gas at a rate in excess of 600 cubic feet per minute per square foot of combustion chamber cross-sectional area, and the combustion air supply means are adapted and adjusted to supply air at a rate suflicient to burn the blast furnace gas.

References Cited by the Examiner UNITED STATES PATENTS Wunsch 158-109 10 6 2,261,904 11/ 41 MoDermott 1587 2,693,140 11/54 Minton 26319 X 3,024,014 3/62 Benson et a1 158109 FOREIGN PATENTS 350,110 3/22 Germay.

CHARLES SUKALO, Primary Examiner. 

1. IN BLAST HEATING APPARATUS COMPRISING A VERTICAL ELONGATED HEAT EXCHANGING CHAMBER FILLED WITH CHECKER WORK OF HEAT ABSORBING MATERIAL AND AN UNOBSTRUCTED COLUMNAR COMBUSTION CHAMBER HAVING AN OUTER WALL, MEANS FOR CONNECTING THE UPPER ENDS ONLY OF THOSE CHAMBER WITH EACH OTHER, COMBUSTION GAS SUPPLY MEANS AND COMBUSTION AIR SUPPLY MEANS, THE IMPROVEMENT COMPRISING A PLURALITY OF GAS BURNERS SET IN THE OUTER WALL OF THE COMBUSTION CHAMBER ONE ABOVE THE OTHER, AT LEAST ONE BURNER BEING A PREMIXING BURNER OF GENERALLY CYLINDRICAL FORM AND HAVING A CHAMBER ADJACENT ITS CLOSED END AND A SMALLER DIAMETER PASSAGE COMMUNICATING THEREWITH AND OPENING INTO THE COLUMNAR COMBUSTION CHAMBER, AN IMPERFORATE AIR INLET CONDUIT OF SMALLER DIAMETER THAN THE PASSAGE EXTENDING THROUGH THE CLOSED END OF THE BURNER INTO THE CHAMBER AND TERMINATING AT ABOUT THE JUNCTION OF THE CHAMBER WITH THE PASSAGE, AND A GAS INLET OF SMALLER DIAMETER THAN THE PASSAGE OPENING RADIALLY INTO THE WALL OF THE CHAMBER, THE PREMIXING BURNER BEING POSITIONED TO PROJECT A FLAME TRANSVERSELY OF THE COMBINATION CHAMBER. 